(Pentafluorophenyl) Group 13 and 15 metal compounds are strong Lewis acids and have many useful industrial applications. In particular, they are useful as catalyst activators in combination with metallocene catalysts in Ziegler-Natta polymerizations and as co-initiators in combination with proton sources and/or carbocation synthetic equivalents for cationic polymerizations.
Despite the utility of (pentafluorophenyl) Group 13 and 15 metal compounds little improvement has been made in their manufacture. Three main strategies have been used for the synthesis of these compounds each possessing drawbacks. One strategy involves the preparation of a pentafluorophenylmagnesiumhalide (Grignard reagent) in an ethereal solvent followed by reaction with a Group 13 or 15 metal halide. These reactions are inefficient in terms of yield. The Grignard reagent is thermally unstable in the absence of an ethereal solvent, has a limited shelf life, and requires special handling. The ethereal solvent also forms a complex with the product and its removal is energy intensive and in some cases it is impossible to remove. Another methodology involves substitution of pentafluorophenyllithium (C6F5Li) for the Grignard reagent in the displacement reaction with the Group 13 or 15 metal halide. This results in improved product yields. Pentafluorophenyllithium is very thermally unstable and in order to avoid explosion it must be prepared and reacted at low temperatures. Reaction is also typically conducted in the presence of an ethereal solvent that must be removed from the end product. Even though yields are improved this method suffers from energy and safety considerations. A third approach for the synthesis of (pentafluorophenyl) Group 13 and 15 metal compounds is transmetallation. This involves reaction of a precursor pentafluorophenyl metal compound (typically mercury, cadmium, or tin) with a Group 13 or 15 metal halide. In some cases yields are good but the precursor pentafluorophenyl metal compounds are toxic. In certain cases coordinating solvents are required for reaction and their complete removal can be difficult. Synthesis of the precursor pentafluorophenyl metal compound itself may require the use of a pentafluorophenyllithium or Grignard reagent. In such a case transmetallation offers no distinct benefit compared to direct reaction of a pentafluorophenyllithium or pentafluorophenylmagnesiumhalide reagent with a Group 13 or 15 metal halide.
Tris(pentafluorophenyl)boron {B(C6F5)3} was first prepared by Massey and Park via reaction of pentafluorophenyllithium and boron trichloride (BCl3) in pentane at −78° C. Not only is this chemistry inherently dangerous to conduct but yields are relatively low and were reported to range from 30-50%. Due to the thermal instability of pentafluorophenyllithium subsequent investigators used pentafluorophenylmagnesium-bromide (BrMgC6F5) in conjunction with the diethyl etherate complex of boron trifluoride {BF3.O(CH2CH3)2} for the preparation of B(C6F5)3. This procedure gives rise to improved yields (c.a., 80%). Although safer from an operational standpoint, removal of the ethereal solvents used in this method requires additional steps such as azeotropic distillation or sublimation and is energy intensive and time consuming.
Following the discovery of B(C6F5)3, several (pentafluorophenyl) Group 15 compounds were prepared, including tris(pentafluorophenyl)phosphine {P(C6F5)3} and tris(pentafluorophenyl)phosphine oxide {OP(C6F5)3}. P(C6F5)3 was prepared in 39.5% yield by reaction of phosphorus trichloride (PCl3) with BrMgC6F5 in ether. This method suffers from low yields. OP(C6F5)3 was prepared in 97.1% yield by oxidation of P(C6F5)3 with sodium dichromate (Na2Cr2O7) in a mixture of sulfuric and acetic acids. Later, both tris(pentafluorophenyl)arsenic {As(C6F5)3} and tris(pentafluorophenyl)antimony {Sb(C6F5)3} in addition to P(C6F5)3 were prepared. This was accomplished by reaction of C6F5MgBr with AsCl3, SbCl3, and PSCl3 in diethyl ether respectively. This method suffers from low product yields {25% for P(C6F5)3, 39% for As(C6F5)3, and 32% for Sb(C6F5)3}. Subsequent researchers substituted pentafluorophenyllithium in place of the Grignard reagent for the preparation of these compounds. This resulted in improved product yields {85% for P(C6F5)3, 75% for As(C6F5)3, and 75% for Sb(C6F5)3}. Due to the thermal instability of the lithium reagent however, these reactions had to be conducted at −78° C. unfortunately. The synthesis of tris(pentafluorophenyl)amine {N(C6F5)3} proved to be more difficult than the other aforementioned (pentafluorophenyl) Group 15 compounds. Other researchers were able to prepare N(C6F5)3 by reaction of HN(C6F5)2 with hexafluorobenzene in the presence of the strong base p-tolylsodium. Reaction was conducted at 230° C. for 42 hours to afford N(C6F5)3 in 24% yield. This procedure suffers from drastic reaction conditions and low yields.
Preparation of the diethyl etherate adduct of tris(pentafluorophenyl)gallium {Ga(C6F5)3.O(CH2CH3)2} from reaction of gallium trichloride (GaCl3) and BrMgC6F5 in diethyl ether is known. Although this procedure gives rise to Ga(C6F5)3.O(CH2CH3)2 in 65% yield, researchers were unable to remove the coordinated diethyl ether. The synthesis of base free Ga(C6F5)3 was not possible until much later. The first disclosure of a method for making base free Ga(C6F5)3 involved the reaction of elemental iodine with Ga(C6F5)3.O(CH2CH3)2 to form uncomplexed Ga(C6F5)3 and an iodine-diethyl ether adduct, the latter being removed by distillation under reduced pressure. The yield of uncomplexed Ga(C6F5)3 as produced by this method has not been disclosed. This method suffers from the use of environmentally unfriendly iodine. A second method for the preparation of uncomplexed Ga(C6F5)3 involves the exchange reaction between B(C6F5)3 and trimethylgallium {Ga(CH3)3}. This strategy purportedly gives rise to high yields of uncomplexed Ga(C6F5)3 but involves the requisite use of expensive and pyrophoric Ga(CH3)3 in addition to consuming valuable B(C6F5)3.
Synthesis of the diethyl etherate complex of tris(pentafluorophenyl)indium {In(C6F5)3.Et2O} is also known. This involved the reaction of BrMgC6F5 with indium trichloride in diethyl ether to give In(C6F5)3.Et2O in 34% yield. No method for removing the complexed diethyl ether was provided. This method suffers from low yields and the inability to form uncomplexed In(C6F5)3. Uncomplexed In(C6F5)3 was first prepared by researchers, who developed three different strategies for manufacture of this compound. The first involved direction reaction of neat IC6F5 with excess In metal. In(C6F5)3 was isolated in a low yield of 31% via sublimation from the reaction mixture. The second method involved reaction of pentafluorophenylmagnesiumchloride with indium trichloride in tetrahydrofuran (THF) followed by treatment of the crude product with dioxane/ether to yield the complex In(C6F5)3.dioxane in 41% yield. Despite the increased yield no means of obtaining uncomplexed In(C6F5)3 was described. A third procedure involved transmetallation of In metal with Hg(C6F5)2. This resultant product mixture was contaminated with metallic mercury and purification required fractional sublimation to ultimately afford In(C6F5)3 in 53% yield. This method suffers from the toxicity of the precursor mercury compound.
Synthesis of the diethyl ether adduct of tris(pentafluorophenyl)aluminum {Al(C6F5)3.O(CH2CH3)2} from reaction of aluminum trichloride (AlCl3) and pentafluorophenylmagnesiumbromide (BrMgC6F5) in diethyl ether is also known. However, attempts at removing the coordinated ether resulted in explosion. The synthesis of base free Al(C6F5)3 was not possible until much later. The first disclosure of a method for making base free Al(C6F5)3 was provided by researchers in 1995. This was accomplished by reaction of Me2AlCl with C6F5Li in hexanes to initially form Me2AlC6F5 which is then heated to 180° C. in vacuo to liberate AlMe3 and generate crude Al(C6F5)3. Recrystallization of the crude reaction product from THF gave the adduct THF.Al(C6F5)3 in 64% yield. This procedure is dangerous to conduct as C6F5Li is thermally unstable and the produced Al(C6F5)3 is energetic and exploded on occasion. An alternative route for the synthesis of Al(C6F5)3 involves the exchange reaction between B(C6F5)3 and trimethylaluminum which is typically conducted in an aromatic hydrocarbon (i.e., toluene). This strategy purportedly gives rise to high yields of base free Al(C6F5)3 (stable in toluene) but involves the requisite use of pyrophoric Al(CH3)3 in addition to consuming valuable B(C6F5)3.
The synthesis of Bi(C6F5)3 by certain methods known. Some researchers prepared this compound from the reaction of C6F5MgBr with bismuth trichloride (BiCl3) in diethyl ether. Yields of Bi(C6F5)3 obtained from this method were low (c.a., 30%). Other researchers prepared Bi(C6F5)3 via transmetallation of bismuth tribromide (BiBr3) with Cd(C6F5)2.diglyme in acetonitrile. Although this procedure improved product yields (71%), it suffers from the use of toxic cadmium compounds. Isolation of uncoordinated Bi(C6F5)3 from this method also requires distillation of diglyme from the product under reduced pressure, a process that is time consuming and energy intensive.
From the foregoing it is clear that there is a need for an improved process for preparing uncomplexed (pentafluorophenyl) Group 13 and 15 metal compounds in a highly efficient manner with improved industrial applicability. Ideally, such a process would be safe to operate and have reduced impact on the environment. The present invention is directed to these, as well as other, important needs.
It is previously known in the art that Group 11 and 12 pentafluorobenzoates can be decarboxylated to yield the corresponding (pentafluorophenyl) Group 11 and 12 metal compounds. Several methods for the synthesis of Group 11 and 12 pentafluorobenzoates have been previously disclosed. One method involves neutralization of pentafluorobenzoic acid with a Group 11 or 12 metal oxide, hydroxide, or carbonate under aqueous conditions followed by dehydration of the reaction mixture. Another strategy involves the reaction of pentafluorobenzoic acid with a Group 11 or 12 metal acetate in an organic solvent followed by the removal of volatiles. A final methodology involves contacting a Group 1 or 2 metal salt of pentafluorobenzoic acid with a Group 11 or 12 metal halide under aqueous conditions followed by dehydration of the reaction mixture.
Since (pentafluorophenyl) Group 11 or 12 metal compounds are readily decomposed by protic materials such as water, pentafluorobenzoic acid, and acetic acid, materials that are typically either liberated and/or used in the synthesis of the Group 11 and 12 pentafluorobenzoates by the aforementioned methodologies, it is important to remove all traces of such materials from the produced Group 11 and 12 pentafluorobenzoates prior to decarboxylation to prevent a reduction in yield. From an environmental and cost standpoint it is most desirable to have a method for preparing Group 11 and 12 pentafluorobenzoates free of protic materials that does not require the use of solvents. The present invention is also directed to these, as well as other, important needs.